Fungus Guard is an anti-fungal and antibiotic, which attacks both types of Fin Rot. Likely, nothing will happen to your fish or plants, if you use either of the options available to you. I would recommend, however, that you only use half the dosage of Fungus Guard. I have never used full dosage. This is especially recommended when dosing Bettas, who are typically more sensitive to medications.

Additionally, neither your snails nor your beneficial bacteria will be effected by the Fungus Guard. All of my snails (Nerites, rabbit snails & assassins - different tanks) have been in tanks where I've medicated with Fungus Guard, and I've never had deaths attributable to it.